P4 Electricity Flashcards
Diode
A non-ohmic conductor that has a much higher resistance in one direction(its reverse direction) than in its forward direction
Light-depending resistor
A resistor whose resistance depends on the intensity of the light incident on it
Light-emitting diode
A diode that emits light when it conducts
Ohm’s law
The current through a resistor at constant temperature is directly proportional to the potential difference across the resistor
Parallel
Components connected in a circuit so the potential difference is the same across each one
Potential difference
A measure of the work done/energy transferred to the lamp by each coulomb of charge that passes through it
Resistance(equation)
Potential difference/Current
Series
Components connected in a circuit in such a way the same current passes through them
Thermistor
A resistor whose resistance depends on the temperature of the thermistor
Electrical current
A flow of electrical charge
Potential difference
The driving force that pushes the charge round
How does the resistance across a component affect the current flowing through a component?
The greater the resistance across a component, the smaller the current that flows(for a given potential difference across the component).
Charge flow =
Current x time(seconds)
Potential difference =
Current x resistance
What measures the current through a test wire?
The ammeter
What measures the potential difference across the test wire?
The voltmeter
How should ammeters always be placed?
In series with whatever you’re investigating
How should voltmeters always be placed in a circuit?
The voltmeter must always be placed in parallel around whatever you’re investigating
Required practical(to investigate the factors affecting resistance)
1) Attach a crocodile clip to the wire level with 0cm on the ruler.
2) Attach the second crocodile clip to the wire e.g. 10 cm away from the first clip. Record the length of the wire between the clips.
3) Close the switch, then record the current through the wire and
the potential difference across it.
4) Open the switch, then move the second crocodile clip, e.g. another 10cm along the wire. Close the switch again, then record the new length, current and potential difference.
5) Repeat this for a number of different oengths of the test wire.
6) Use your measurements of current and potential difference to calculate the resistance for each length of wire.
7) Plot a graph of resistance against wire length and draw a line of best fit.
What should be the results of the practical investigating the factors affecting resistance?
The graph should be a straight line through the origin - showing the longer the wire, the greater the resistance.
Possibly systematic errors(in resistance practical).
The first clip isn’t attached exactly at 0cm, so all the length readings are a bit out(seen if the graph doesn’t go through the origin).
How to ensure accuracy(in resistance practical).
1) Thin wire will give best results.
2) Ensure the wire’s as straight as possible so the length measurements are accurate.
3) The wire may heat up during the experiment, which will affect its resistance. Leave the switch open for a bit between readings to let the circuit cool down.
At a constant temperature, how does current affect potential difference?
At a constant temperature, the current flowing through an ohmic conductor is directly proportional to the potential difference across it.
Examples of ohmic conductors
Wire(at constant temperature)
Resistor(at constant temperature)
In which components, does the resistance change as the current through them changes?
A diode or a filament lamp